Diablo 3 was announced last weekend. Cue excitement, anticipation and - in my case - a re-install of Diablo 2. I caught up with Diablo 3's Lead World Designer Leonard Boyarsky and chatted about designing Diablo 3, how the random sections will work and why co-op - hurrah! - is so important.

So what does a Lead World Designer do then?I'm responsible for lore, history and world creation. The role goes across lots of departments from quest design to artists. Or as I like to tell my wife, I'm a bit like a God. No seriously, it's a wide encompassing role.

Why the delay in announcing Diablo 3?

I have only been at the company for two and half years so can't speak about what happened before then but I know since I have been involved we have been working flat out to create something very special. People have been waiting a long time for this game. People expect a lot from us and we have to deliver. We always like to make our announcements feel like a big event so we want to have something fantastic to show. And any delay is primarily because we want to deliver this quality of game.

What audience are you going for with Diablo 3? Newcomers? WoW players? Or just fans of the original games?

One of the great things about Blizzard as a company is that we if we make a fantastic game then people will play them. If Diablo 3 is as good as we think it will be then we will attract new players. But the Diablo fans are vital to us. They are the guys waiting for the game and we want to make them happy. We want to make it accessible but need to make sure the gameplay is fun and deep enough for fans too. We test it with all kinds of players. WoW dragged in new players who had never played an MMO before and I think Diablo 3 could be equally inclusive.

Diablo 3 sounds like it will be more structured and quest driven than the older games?

It's a balancing act. We don't want to make it feel too structured and it needs to remain open ended. But we want players to get interested and immersed in the story and lore. This is something we can definitely improve on from Diablo 2. Diablo 2 was great with action and the story was ok but the questing and justification for action was often quite weak. We don't want to make it feel you are being pulled along or hemmed in but we want to make it feel like something big is going on. So yes, a real balancing act.

So how do you fit the random settings, which Diablo is well known for, in with the more structured game you appear to be planning?This is where the "adventures" come in. Even in the previous games, where there was a lot of random elements, there were still specific characters in specific towns. But to keep as much of a random feel as possible we have these things called adventures. These are quests or scripted events or anything that can fit into slots in the world. These will be randomly placed and may appear in your game or may not. They could be little scenarios, or self contained events. We can chain them together and say if this spawns in this game then this will also happen. But your friend may not even see any of them in his game. But we're not afraid to put the work into that as we think people will play this game twenty times in a row because that is what the randomness is there for. So if you don't see it on your first go you may see it on your fifth. And that makes people want to play even more. And now we have new classes, with class specific quests and different NPC reactions to each class. This just adds to the variety and there is lots that can be mixed and matched. The adventures are like the flavour on top of the fixed action. It

What changes are you planning in art design, setting etc?

We want it to be familiar to fans of the original games but things have come a long way since then. The first Diablo game was s fairly conventional fantasy world with a little bit of horror. Diablo 2 started pushing the envelope a little and Diablo 3 will bring more and push things further. If we get more distinctive with styles and history it gives people more to grab onto and so get further connected with their characters.

What do you think of the clones that have sprung up since Diablo 2 such as Mythos, Titan Quest, Hellgate etc?

We play a lot of games, we're all gamers. I know people on the team have played those games. We look at all games and think "we like that" or "we don't like that". But then all developers do that. Yes, I'm being politically correct here!

How important is online to Diablo 3?

Very important. I see it as playing a single player campaign in a multiplayer setting. Like really getting that feeling of sitting around with your friends playing a tabletop game. You can join in any time with your friends, although this obviously affects the game. For example Non Player Characters (NPC) will have different reactions to different classes. So very few of them will know that the Witch Doctor exists while the Barbarian is very common. This affects how they react to you, could easily change the team dynamic. But yes, we are going to really nail the player experience with Battle.net and make it easy to play online.

How will co-op work in Diablo 3?

We have had some very animated discussions about this. We all care a lot. But part of it is just trying to convey what we can do in this area. There are so many facets to it. What if your friend is level 20 and you are level 3. If the level 20 leaves takes you to an area you can't cope with and then leaves you obviously die. Will your corpse remain there? There are a lot off issues to solve but ultimately we want to remove all the barriers that prevent you from getting together and playing with your friends. That's our goal.

What about the Mac version. Will it be released at the same time? Will Mac and PC players be able to play together?We haven't announced release dates yet but there will be a Mac version. Will Mac and PC gamers be able to play together? (laughs)That's a great idea. We'll see.